1. Field of the Invention
The present invention relates to a pattern forming method for forming a pattern on an insulating board by using a functional material in the manufacturing process of, for example, flat panel image display device, wiring board, or IC tag.
2. Description of the Related Art
Conventionally, the technology of photolithography has been playing a principal role as the technique for forming a fine pattern on the surface of a board material. This technology of photolithography has been enhancing the resolution and performance, while a tremendous investment is needed in the manufacturing equipment, and the manufacturing cost is soaring along with enhancement of resolution.
On the other hand, in the manufacturing field of semiconductor devices, image display devices and others, the demand for lower price is mounting along with the request for improvement of performance, and such request can be no longer satisfied by the existing technology of photolithography. In this background, a recent attention is being focused on the pattern forming technology making use of digital printing technique.
By contrast, for example, the ink jet technology comes to be realized as patterning technology simple in apparatus and characterized by non-contact patterning, but it is limited indeed in enhancement of resolution and productivity. In this respect, the technology of electrophotography, especially electrophotography using liquid toner is excellent in possibility.
By utilizing this technology of electrophotography, various methods have been proposed for forming phosphor layer, black matrix or color filter on the front board for flat panel display (see, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 2004-30980 and 6-265712).
However, in the field of flat panel display, the demand for higher resolution is escalating, and it is requested to form a pattern of higher resolution at higher precision of position. Actually, however, it is hard to meet the needs by the method of electrophotography. This is because the resolution of the writing optical system is about 1200 dpi at most, which is insufficient for resolution or positioning. Also, it is not possible to realize a broad writing optical system applicable to the recent wide screen of display.
On the other hand, it has been proposed to form a pattern of phosphor or the like on a front glass for display, by using an electrostatic printing plate having patterns different in electric resistance preliminarily formed on the surface, instead of the phosphor, developing the patterns by applying a liquid toner on the plate, and transferring the pattern images to the glass plate (see, for example, Jpn. PCT National Publication No. 2002-527783).
However, as a result of intensive studies and experiments by the present inventors, the following intrinsic problems have been discovered also in this method.
First, the developed image by liquid toner is generally about 1 μm or less in film thickness, and it is not suited to forming of a thick film such as phosphor or color filter of the display device, and thus a new idea is needed for forming a thick film of high definition.
Besides, if a corona charger is used when transferring the developed image on the glass plate, the corona charge may leak through the glass surface, and the transfer characteristics tend to be unstable. In addition, the spatial charge is likely to be accumulated inside the glass, and thus it has been difficult to form a transfer electric field capable of overcoming this spatial charge by the corona discharge. Further, when the developed image of one color is transferred, this problem becomes more obvious, and it has been very difficult to transfer the developed images of the second color and third color on the glass plate.